Responsible organisation

Swedish Polar Research Secretariat

Abstract [en]

In order to reconstruct the temperature of the North Greenland Ice Core Project (NGRIP) site, new measurements of delta N-15 have been performed covering the time period from the beginning of the Holocene to Dansgaard-Oeschger (DO) event 8. Together with previously measured and mostly published delta N-15 data, we present for the first time a NGRIP temperature reconstruction for the whole last glacial period from 10 to 120 kyr b2k (thousand years before 2000 AD) including every DO event based on delta N-15 isotope measurements combined with a firn densification and heat diffusion model. The detected temperature rises at the onset of DO events range from 5 degrees C (DO 25) up to 16.5 degrees C (DO 11) with an uncertainty of +/- 3 degrees C. To bring measured and modelled data into agreement, we had to reduce the accumulation rate given by the NGRIP ss09sea06bm timescale in some periods by 30 to 35 %, especially during the last glacial maximum. A comparison between reconstructed temperature and delta O-18(ice) data confirms that the isotopic composition of the stadial was strongly influenced by seasonality. We evidence an anticorrelation between the variations of the delta O-18(ice) sensitivity to temperature (referred to as alpha) and obliquity in agreement with a simple Rayleigh distillation model. Finally, we suggest that alpha might be influenced by the Northern Hemisphere ice sheet volume.